1. Field of the Invention
The present invention relates generally to gas, oil and gas/oil fired water heaters and boilers of the type utilizing a submergible combustion chamber and to an improved tank design for such a water heater or boiler.
2. Description of the Prior Art
Prior art water heaters of the type under consideration have typically provided for the flow of hot gas through a series of tubes which are mounted in vertical fashion between top and bottom support plates within the water heater tank. In this discussion, the term "water heater" will be understood to encompass both water heaters and "boilers" of the type utilized for commercial/industrial use, as well as for residential use. Water was circulated into and out of a chamber in the prior art device located between the support plates. The water contacted and circulated about the exterior of vertical tubes to effect heat transfer to heat the water.
The typical prior art gas, oil or gas/oil-fired water heater featured a non-pressurized external combustion chamber. The location of the combustion chamber on the exterior of the water heater resulted in lost heat and lower thermal efficiency. Also, the tubes and support plates were not easily accessible which generally required disassembly of the entire tank for maintenance and replacement.
In U.S. Pat. Nos. 4,465,024 and 4,545,329, both assigned to the assignee of the present invention, a water heater design was shown which featured a submergible, pressurized combustion chamber so that all combustion took place in the water heater tank interior in a chamber surrounded by water. The resulting design decreased heat loss and increased the thermal efficiency of the water heater in the range of 83% (fuel to water) and above. ANSI standard Z.21.10.3 outlines the accepted industry method of testing thermal efficiency of a water heater.
In spite of such improvements, a need continued to exist for a water heater design with a thermal efficiency exceeding that achievable by the previously described submerged combustion chamber alone. In U.S. Pat. No. 4,938,204, a further improvement to the previous designs was disclosed. In the '204 patent, a water heater design was shown characterized by a thermal efficiency (fuel to water) of 98% and above. This design included a closed tank containing water under pressure with a side wall having a primary side wall opening. A submergible, pressurized combustion chamber was installed within the primary sidewall opening so that all of the heating surfaces were submerged in the water under pressure at a first location within the tank. A secondary heat exchange means was provided for preheating water at a second location which is below the first location within the closed tank. Passage means conducted the products of combustion generated in the submerged combustion chamber to the secondary heat exchange means so that cooler water entering the tank is preheated by the secondary heat exchange means prior to contacting the external heating surfaces of the submerged combustion chamber.
In one embodiment of the invention described in the '204 patent, the two tank locations were actually separate tanks which were separated by a divider plate. A cross-over tube provided fluid communication to allow water to pass from the preheat zone to the primary heat exchange zone. Using this design, a 99% thermal efficiency was verified by independent third party testing.
Despite the advantages afforded by the design shown in the '024 patent, a need existed to provide a simplified tank design while maintaining the increased thermal efficiency provided by primary and secondary heat exchange compartments. Accordingly, the present invention provides a single tank design having a novel combustion chamber arrangement which divides the single tank into a primary and secondary heat exchange compartments.
The present design also features a removable combustion chamber which forms a sliding seal with respect to the surrounding water heater tank interior when the combustion chamber is installed within an end opening of the tank.
The water heater design of the invention is characterized by a thermal efficiency (fuel to water) of 98% and above while offering a simplified design with fewer components which occupies less space than the designs of the prior art.